move get functional test material(openj9 tests) to functional/build.xml

In aqa-tests we have openjdk, system, perf, external, functional tests category. Each test category follows a similar structure and manage its own test material, i.e. with build.xml to gather test material ( git clone, curl, wget). This approach ensures simplicity, extensibility and low coupling.

Functional tests ( openj9 tests) are gathered differently [ getFunctionalTestMaterial() in get.sh by passing in extra parameters](https://github.com/adoptium/aqa-tests/blob/master/get.sh#L615), which due to initially TKG was part of openj9. As TKG has its own repo it's time to move this process to functional/build.xml. This way when a new feature is enabled functional tests won't need to be considered differently, which might be missed, need extra tests and costs more. For example https://github.com/adoptium/TKG/pull/651

Start with getFunctionalTestMaterial() in get.sh and compare how the other test categories gather material through their build.xml files. Move the OpenJ9 functional-test material handling to functional/build.xml, then verify that functional tests still obtain the same material without the special get.sh parameters.

Written by the indexing model from the issue text.